The Colorado Supreme Court appeared doubtful on Tuesday that the failure to formally designate a witness as an expert in front of the jury rose to the level of mistake that would require a new murder trial for the defendant.

Denver jurors convicted Pete Paul Martinez of stabbing 77-year-old Lewis Easterday to death near Cheesman Park in 2016. Martinez admitted to the crime, but asserted he was not guilty by reason of insanity, insisting god had guided his actions. A court-appointed psychologist evaluated Martinez and found him sane.

But last year, the Court of Appeals ordered a new trial for Martinez because of an apparent oversight by the trial judge and the parties. In contrast to the typical practice in Colorado — and in contrast to how the other expert witnesses in Martinez’s case were handled — the prosecution did not offer the psychologist as an expert, nor did the judge accept him as such in front of the jury.

The appeals court’s majority saw the process as more than just a formality, but some members of the Supreme Court seemed skeptical, given the psychologist’s undisputed expertise and the defense’s lack of objection.

“I’m not a fan of accusing anybody of gamesmanship, but I am concerned about the risk here,” said Justice Richard L. Gabriel during oral arguments. “Everybody went through this trial knowing this person was an expert. And now, after the fact, it feels a little like a gotcha: ‘Didn’t do the qualification. Let’s reverse a first-degree murder conviction.'”

In convicting Martinez, jurors signaled they believed psychologist Charles Harrison’s testimony that Martinez was sane. Under the rules of evidence, a witness who is “qualified as an expert” may offer their opinions, with trial judges acting as gatekeepers for reliability. But there is no rule requiring the specific act of offering a witness as an expert and the judge accepting them as such in front of the jury.

By 2-1, however, a Court of Appeals panel believed District Court Judge A. Bruce Jones’ failure to do so was worthy of reversal, given how important Harrison’s opinions were to the case.

“Dr. Harrison’s testimony was inadmissible because it was expert evidence and the trial court did not determine that he was an expert witness qualified to give expert testimony and did not make specific findings supporting such a determination,” wrote Judge Anthony J. Navarro for himself and Judge Timothy J. Schutz.

Judge Ted C. Tow III dissented, noting the parties had treated Harrison as an expert all along — and even called him an “expert” when speaking during trial. Tow added that he believed the defense’s failure to object was purposeful, meaning Martinez had given up his right to challenge the alleged error on appeal.

To the Supreme Court, the prosecution noted Martinez’s case was an outlier, as parties typically follow the formal protocol. Senior Assistant Attorney General William G. Kozeliski advocated for a rule that would allow, but not require, trial judges to accept witnesses as experts on their own initiative when the parties neglect to ask for it.

“Assuming there is an error, it’s a procedural step,” he said. “It’s not that the testimony is inadmissible. It’s that you didn’t do this extra step to focus the testimony or to tell the jury how to analyze it.”

“At the very least, that seems to be the tradition in Colorado state courts,” observed Justice William W. Hood III. “Given that that has been the tradition for so long, why shouldn’t we say that has effectively become part of the gatekeeping function of the trial court and, therefore, this needs to happen?”

Justice Carlos A. Samour Jr., a former trial judge, explained there was a reason for parties to formally offer witnesses as experts.

“That’s because the prosecutor is presenting the testimony. I get that the court appointed the witness. But it’s the prosecutor calling the witness. It’s the prosecutor asking the jury to believe that testimony,” he said.

To that end, “are you saying that that procedural step carries no weight whatsoever?” Chief Justice Monica M. Márquez asked Kozeliski. “Isn’t it that very step that, in fact, ensures all the qualifications have been met?”

Although Martinez’s lawyer agreed the usual practice for qualifying experts is essential to informing jurors about how to use opinion testimony, Justice Brian D. Boatright wondered why reversing Martinez’s murder conviction was appropriate.

“If we affirm the Court of Appeals and it goes back for a new trial, other than the ‘Your honor, I offer Dr. Harrison as an expert in forensic psychology’ and the court says, ‘So admitted,’ what will be different?” he asked.

The case is People v. Martinez.